You can’t completely break something for a long time and expect people to jump right back when you fix it. I, like many others, had to go elsewhere when kde3 became impractical to keep running and kde4 was completely broken.
+1 this. I'm sick of distributions which I've gotten used to and liked who suddenly throw themselves (and my productivity) off a GUI cliff. I don't care if you're putting in place the building blocks for some super duper new GUI, I use my computers to get things done and don't like having a "WTF?" moment when I upgrade.
I used and really liked KDE for a long time, and along came 4.x . Suddenly I was left with a half working GUI, and was told that "well you shouldn't have upgraded should you?" and "it'll get better when we fix all the bugs". This is my problem now is it?
MS are about to run into the same issue with Windows 8. Taking a well known and, maybe not loved but tolerated, GUI paradigm of a desktop and discarding it. It's going to cause chaos and resentment amongst their user community, many of whom will look at alternatives.
I greatly respect everyone who contributes to open source, and I know you put your heart and soul into it, but for most of us our computers are not toys that we sit and tinker with endlessly to display snazzy new GUI effects, they are the tools we use to get things done. Once you lose the trust of the user that they can rely on you to provide a stable and easy to use OS you will have an incredibly hard job getting them back.